1. Field of the Invention
The present invention relates to an antibiotic additive and an ink composition comprising the same. More particularly, it relates to an antibiotic additive showing antibiotic effects provided by binding of a compound having antibiotic effects to a wetting agent or storage stabilizer in an ink composition and an ink composition comprising the same.
2. Description of the Related Art
The antibiotic additive according to the present invention and the ink composition comprising the same may be applied to, for example, coatings, paints, inks, and the like. Of them, the ink compositions for a printer, particularly ink compositions for an ink jet printer are representative. Instances of applications as an ink composition for an ink jet printer will be concretely described below.
The printing method by a printer is largely divided into two types: non-impact printing and impact printing. Ink jet printing is a non-impact printing method and has advantages such as a low noise level, as compared to the impact printing methods, and may more readily realize colors, as compared to laser beam printers.
The ink jet printing methods are of two types: continuous stream and drop-on-demand. In continuous stream ink jet methods, ink is ejected in a continuous stream under pressure through an orifice or nozzle. The ejected ink is broken up into droplets and perturbed at a fixed distance from the nozzle. The droplets, while being dispersed, are charged in accordance with digital data signals. The charged droplets pass through an electric field in which the trajectory of each droplet is adjusted to be circulated, or is directed to a gutter on a specific location of a recording medium. In a drop-on demand method, an ink droplet is expelled from a nozzle directly onto a specific location of a recording medium in accordance with digital data signals. Thus, a droplet is not formed or expelled unless it is ejected onto a recording medium.
The drop-on-demand methods are much simpler than the continuous stream systems since the drop-on-demand methods do not require ink recovery, charging or deflection. There are two types of drop-on-demand ink jet methods, one of which is the thermal ink jet type (also called bubble jet type) and the piezoelectric inkjet type.
In the thermal ink jet methods, ink is ejected using a pressure generated by expansion of bubbles formed by heating the ink. The thermal ink jet methods produce droplets having a high speed and allow a very close distance between nozzles. By introduction of the thermal ink jet methods, a printer may operate at a high speed and at low cost while having a simple structure, as compared to using the continuous stream printing methods.
On the other hand, according to the piezoelectric ink jet methods, ink is ejected under a pressure generated by a piezoelectric plate, which may dynamically transform droplets by electricity. Thus, in the piezoelectric ink jet methods, the piezoelectric plate with a relatively large size interferes with a close distance between nozzles. Also, such a physical limit of the piezoelectric plate ultimately reduces the speeds of the ink droplets. A low droplet speed severely reduces resistance to the droplet speed change and thus, affects provision of high quality prints. Further, the drop-on-demand system, when applying a piezoelectric ink jet method, has a disadvantage of a low printing speed.
Meanwhile, the dot size of the ink jet printers gets smaller, and there is a need for a high quality print at a high resolution. In order to obtain a smaller dot size, a print head of an ink jet printer is required to have a smaller nozzle opening. However, such a small nozzle opening may be readily clogged, and the performance of ink jet droplets depend on precipitations which may exert influence on sizes of the droplets. It is already known that components of an ink composition may cause nozzle clogging, and a wetting agent is usually added to inks for the ink jet printer to prevent the clogging.
Also, an ink composition for use in an ink jet printer comprises basically a colorant, a solvent and other additives. However, for an application in color printing using an ink jet printer, such an ink composition should have properties that faciliate jetting on a recording medium as intended and, after being jetted, be adsorbed or absorbed on the recording medium to form an expected image. Therefore, the ink composition comprises various additives to show proper performance in viscosity, surface tension, optical density, dot uniformity, jetting stability, drying time, bleeding, storage stability, color properties (hue, lightness, saturation), affinity to a printer head and a recording medium, smear fastness, water fastness of an image, and the like. It has been proposed to use a nitrogen-containing heterocyclic compound such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone as an additive to realize the storage stability of an ink composition (U.S. Pat. Nos. 5,108,503; 5,858,075; 5,980,622; 5,990,202; 6,057,384; 5,641,346; 5,972,086; 6,039,796; 6,095,645). According to the disclosures of the above listed patents, when a nitrogen-containing heterocyclic compound such as 2-pyrrolidone, N-methyl pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone is used as an additive, it is possible to obtain effects of improving storage stability, wettability and drying properties.
When a dye is used as a colorant in an ink composition for an ink jet printer, the water fastness and light fastness of the ink are impaired. Therefore, use of such a dye is limited. On the other hand, where a pigment is used as a colorant, the water fastness and the light fastness of the ink are superior to a water fastness and a light fastness of an ink using a dye. Meanwhile, an ink composition comprising a dye or a pigment as a colorant has problems of deterioration in ink properties due to propagation of bacteria and thus, storage stability. Therefore, it has been proposed to add a special antibiotic to suppress the propagation and growth of bacteria. However, the antibiotics added in an ink composition may bond to other additives in the ink composition to form a macromolecule, which significantly increases the nozzle clogging by ink coagulation and makes it difficult to ensure uniformity of the ink. Also, when an antibiotic which can inhibit such side effects is used, problems occur in that storage stability for a long period of time may be deteriorated, owing to the weak antibiotic properties, and optimal color properties cannot be attained since it is difficult to select a dye or a pigment with an excellent compatibility with the antibiotic.